Sleep apnea generally refers to the cessation of breathing during sleep. It is generally recognized that there are two types of sleep apnea. The more common type of sleep apnea is obstructive sleep apnea (OSA), which is characterized by repetitive pauses in breathing during sleep due to the obstruction and/or collapse of the upper airway, usually accompanied by a reduction in blood oxygen saturation.
The less common type of sleep apnea, central sleep apnea (CSA), refers to a neurological condition causing cessation of substantially all respiratory effort during sleep. One common form of central sleep apnea, commonly known as Cheyne-Stokes respiration (CSR), is characterized by a breathing pattern that begins shallow and infrequent and then increases gradually to become abnormally deep and rapid, before fading away completely for a brief period. Breathing may stop altogether for an extended time period, before the next cycle of shallow breathing begins. CSR is common in patients with congestive heart failure (CHF). Some patients have a combination of OSA and CSA, which is commonly known as mixed sleep apnea.
Cycles of sleep, snoring, obstruction, arousal, and sleep may occur many times throughout the night. The arousal associated with sleep apnea invokes the sympathetic nervous system, which acutely causes increased heart rate and blood pressure. Chronically, episodes of apnea and arousal may lead to systemic hypertension, pulmonary hypertension, ischemic heart disease, stroke, and cardiac arrhythmias. Further, such episodes of apnea and arousal can negatively affect the status, progression, and outcomes of previously existing conditions, such as CHF.